1. Field of the Invention
The present invention relates to a cap device having a torque mechanism to close a tank opening with a preset level of rotational torque.
2. Description of the Related Art
A fuel cap for a fuel tank of an automobile has, for example, a known structure described in JP No. 2000-344266A. FIG. 28 is a decomposed perspective view showing a torque mechanism of a prior art fuel cap 100. The fuel cap 100 includes a casing main body 110, a cover 120 with a manipulation structure for rotational operations, and a torque mechanism element 122 formed on the cover 120, a torque plate 140 with torque arms 142 that are formed as cantilevers and respectively have torque engagement elements 142a, and a spring 132. When a rotational torque of the cover 120 in a closing direction exceeds a preset level, the manipulation structure engagement element 122 is released from the torque engagement elements 142a to give a click. In response to rotation of the cover 120 in an opening direction, on the other hand, the manipulation structure engagement element 122 engages with the torque engagement elements 142a from the opposite direction and bends the torque arms 142 with a smaller force than the force in the rotation in the closing direction. The manipulation structure engagement element 122 is thus released from the torque engagement elements 142a with a smaller force to be returned to its initial state and integrally rotates the cover 120 and the casing main body 110 via another engagement means to open the fuel cap 100.
In a closing operation of the fuel cap 100, the manipulation structure engagement element 122 of the cover 120 rides over the torque engagement elements 142a of the torque plate 140 to give a click. This proves that the fuel cap 100 is clamped with a torque of a preset level. This arrangement enables the fuel cap 100 to be clamped with a fixed torque, regardless of the resilience of a gasket and other related elements.
This prior art torque mechanism 130 reduces the bending force of the torque arms 142 and thereby the force required for the release of engagement when the positional relation between the manipulation structure engagement element 122 and the torque engagement elements 142a is returned to their initial state in an opening operation of the fuel cap 100. The click or another engagement sound may cause the user to feel uneasy.